I am sharing an internet connection with my friend using a D-link DSl-2750U wireless router and my network cars is Atheros AR9285. Recently I am unable to connect to the network sometimes.
What could be the problem?iwconfig gave the following output:

It is best to set your router to just wpa2 encryption if you have that option.

The signal strength is to low on both networks that you have listed to be able to connect too, but the first set of commands I gave you to run usually helps with that to some extent. You may need to move closer to your router to be able to connect especially if there are walls or something blocking the signal.

Your device is ar9285 with linux drivers it has the worst signal strength of all the devices in this series from my experience so you will not be able to get very far from your router no matter what you do.